THE CONCEPT OF EVOLUTION 599 



body of facts that demonstrated that evolution had occurred, and formu- 

 lating his arguinents for natural selection. In 1857 he submitted a draft 

 of his theory to a number of scientific friends for comment and criticism. 

 Alfred Russell Wallace, a naturalist and explorer who was studying the 

 flora and fauna of Malaya and the East Indies, was similarly struck by 

 the diversity of living things and the peculiarities of their distribution. 

 Like Darwin, he happened to read Malthus' treatise and came inde- 

 pendently to the same conclusion, that evolution occurred by natural 

 selection. In 1858 Wallace sent a manuscript to Darwin, and asked him, 

 if he thought it of sufficient interest, to present it to the Linnaean 

 Society. Darwin's friends persuaded him to present an abstract of his own 

 work along with Wallace's paper and this was done at a meeting of the 

 Linnaean Society in July, 1858. Darwin's monumental On the Origin of 

 Species by Means of Natural Selection was published in November, 1859. 

 The time was ripe for the formulation and acceptance of the theory 

 of organic evolution. The publication of Lyell's Principles of Geology^ 

 and the subsequent acceptance of the idea of geologic evolution, the 

 publication of Malthus' ideas on population growth and pressure and 

 the struggle for existence, together with the vast accumulation of in- 

 formation about the distribution of living and fossil forms of life, and 

 studies of comparative anatomy and embryology, all showed the inade- 

 quacy of the theory of special creation. Because the time was ripe, Dar- 

 win's theory rapidly gained acceptance. 



298. The Theory of Natural Selection 



Darwin's explanation of the way in which evolution occurs can be 

 summarized as follows: 



1. Variation is characteristic of every group of animals and plants, 

 and there are many ways in which organisms may differ. (Darwin did 

 not understand the cause of variation, and assumed it was one of the 

 innate properties of living things. VV^e now know that inherited varia- 

 tions are caused by mutations.) 



2. More organisms of each kind are born than can possibly obtain 

 food and survive. Since the number of each species remains fairly con- 

 stant under natural conditions, it must be assumed that most of the 

 offspring in each generation perish. If all the offspring of any species 

 remained alive and reproduced, they would soon crowd all other species 



from the earth. 



3. Since more individuals are born than can survive, there is a 

 struggle for survival, a competition for food and space. This contest 

 may be an active kill-or-be-kiUed struggle, or one less immediately 

 apparent but no less real, such as the struggle of plants or animals to 

 survive drought or cold. This idea of competition for survival in an 

 overpopulated world was derived from Malthus. 



4 Some of the variations exhibited by living things make it easier 

 for them to survive; others are handicaps which bring about the ehmina- 

 tion of their possessors. This idea of "the survival of the fittest is the 

 core of the theory of natural selection. 



